The present invention relates to a cathode ray tube (CRT) and more particularly, to a CRT that can effectively enhance electron beam deflection efficiency.
Generally, CRTs include a panel having an inner phosphor screen, a funnel having a cone portion, and a neck having an electron gun therein, which are sequentially connected to each other. A deflection yoke is mounted around the cone portion of the funnel to form horizontal and vertical magnetic fields there. In this structure, electron beams emitted from the electron gun are deflected through the horizontal and vertical magnetic fields from the deflection yoke, and land on the phosphor screen.
Recently, CRTs have been employed for use in highly sophisticated electronic devices such as high definition television (HDTV) and OA equipment.
On the one hand, in these applications, the power consumption of the CRT should be reduced to obtain good energy efficiency. Additionally, magnetic field leakage due to power consumption should be reduced to protect the user from a distorted magnetic field. In order to meet these requirements, it turns out that the power consumption of the deflection yoke, which is the major source of power consumption, should be reduced in a suitable manner.
On the other hand, the deflection power of the deflection yoke should increase in order to realize a high brightness and resolution of display images on the screen. Specifically, higher anode voltage is needed for enhancing the brightness of the screen and, correspondingly, higher deflection voltage is needed for deflecting the electron beams accelerated by the increased anode voltage. Furthermore, a higher deflection frequency is needed for enhancing resolution of the screen, along with the requirement of increased deflection power. In addition, in order to realize relatively flat CRTs for more convenient use, wide-angled deflection should be performed with respect to the electron beams. Wide-angled deflection also requires increased deflection power.
In this situation, there are needs for developing techniques for allowing CRTs to retain good deflection efficiency while constantly maintaining or reducing the deflection power.
Conventionally, a technique of increasing the deflection efficiency positions the deflection yoke more adjacent to the electron beam paths. The positioning of the deflection yoke is achieved by reducing a diameter of the neck and an outer diameter of the funnel adjacent to the neck. However, in such a structure, the electron beams to be applied to the screen corner portions are liable to bombard the inner wall of the funnel adjacent to the neck. (This phenomenon is usually called the xe2x80x9cbeam shadow neckxe2x80x9d phenomenon or briefly the xe2x80x9cBSNxe2x80x9d phenomenon.) Consequently, the phosphors coated on the corresponding screen corner portions are not excited and it becomes difficult to obtain good quality screen images.
It is an object of the present invention to provide a CRT that can effectively enhance electron beam deflection efficiency with minimized deflection power.
This and other objects may be achieved by a CRT including a panel with an inner phosphor screen and a rear portion. A funnel is connected to the rear portion of the panel. The funnel is sequentially provided with a body having a large-sized end and a small-sized end, and a cone portion having a large-sized end and a small-sized end. The large-sized end of the body is sealed to the rear portion of the panel. The small-sized end of the body meets the large-sized end of the cone portion at a point. The meeting point of the body and the cone portion is an inflection point of the funnel. A neck is sealed to the small-sized end of the cone portion. An electron gun is fitted within the neck to produce electron beams. The electron gun has a final accelerating electrode. A deflection yoke is mounted around the cone portion of the funnel. The funnel is structured to satisfy the following condition: 1.16xe2x89xa6((D/2)/tan("psgr"/2))/(FGxe2x88x92TN)xe2x89xa61.35 where D indicates the size of an effective area of the phosphor screen, FG indicates the distance between the large-sized end of the body and the final accelerating electrode of the electron gun, TN indicates the distance between the small-sized end of the cone portion and the inflection point of the funnel, and "psgr" indicates the electron beam deflection angle.
The effective screen size D is 17 inches or more, and the electron beam deflection angle is 100 degrees or more. The cone portion may be formed either with a substantially circular sectional shape uniformly proceeding from the large-sized end to the small-sized end, or with a sectional shape varying from a circle to a non-circle shape, such as a rectangle, while proceeding from the small sized-end to the large-sized end.